Looked at this a few days ago and best guess it was a Suntrekker.
Note rear leg set up with this suntrekker
In the past I've seen them brought up to date with better interiors, but this one
(if that's what it was) has had some bodywork modified,
roofline at front, rear wall & headboard has a couple of windows instead of one.
Because they are fibreglass and unless damaged seldom leak, they make excellent base projects, and that might be case here